For over 50 years, shrouded or nozzled propellers have been in use by the marine industry as a means of propulsion for slow speed craft such as tug boats, tankers, river pushboats and floating platforms or docks. Because of their configuration and size, this kind of craft use high pitch, slow RPM propellers (usually less than 200 RPM) and the adaptation of a shroud type enclosure has resulted in an improvement in thrust over a non-enclosed propeller of the same pitch and which diameter, turning at the same RPM. With the introduction of high speed motorboats by the recreational boating industry for water skiing, fishing and the like, the use of high RPM motor drives have been necessary to propel such craft at speeds of 50 miles per hour or better (with propellers rotating at speeds up to 5000 RPM). To date, numerous devices, such as; ring band guards, screens and propeller tunnels, have been tried for increasing thrust and for providing safety from the exposed propeller, with the result of increased drag, reduced performance and the dissatisfaction of their operators, who generally have refused their use.
The U.S. Coast Guard, National Boating Safety Advisory Council and numberable Audubon groups have requested the development for these high speed motorboats of a safety guard for the exposed propellers in order to protect swimmers and water skiers, as well as underwater wild live, such as, the endangered manatee and plant growth that is otherwise needed as food and habitat for other local wild live.
The propeller safety shroud of this invention protects exposed people and wild life against harm and provides a simple, low cost device that can easily be installed on existing and which new drive systems and will also improve the craft's performance.